Hitherto, in the field of nails, coating layers have been formed on a nail in multiple layers. Specifically, a base coat agent is applied on the nail to forma coating layer and then a photocurable composition (UV nail gel) is further applied thereon. A solvent-based base coat agent containing nitrocellulose as a main component is disclosed in WO 2000-076366 A1. In addition, a photocurable artificial nail composition which is a base coat agent is disclosed in JP 2014-23590 A (corresponding to US 2014/030199 A).